A bimorph piezoelectric actuator is available as one type of piezoelectric actuator.
The bimorph piezoelectric actuator is an electronic component which utilizes, as a mechanical drive source, a bimorph piezoelectric element (hereinafter also called a “bimorph element”).
The bimorph element has a structure where two thin plates of piezoelectric ceramic polarized in a thicknesswise direction are laminated together; planar electrodes are embedded in adhesion surfaces of the respective thin plates of piezoelectric ceramic; and at least one electrode is attached to each of the front and back surfaces (outwardly-exposed principal surfaces) of each of the thin plates of piezoelectric ceramic.
Piezoelectric ceramic is a ceramic material which possesses a piezoelectric effect characteristic and is obtained by adding barium titanate, strontium titanate, lead zirconate titanate (PZT), lithium niobate (LiNbO3), or the like, to alumina (aluminum oxide), magnesia (magnesium oxide), silica (silicon dioxide), or the like, which is a common ceramic material, and sintering the mixture.
When a voltage is applied to the respective thin plates of piezoelectric ceramic constituting the bimorph element, one thin plate of piezoelectric ceramic extends by means of a piezoelectric effect, and the other thin plate of piezoelectric ceramic contracts by means of the same. As a result, a bend (flexion) arises in the bimorph element, and displacement arises in an end (a movable end) of the bimorph element. The displacement having arisen in the end (movable end) of the bimorph element can be utilized for mechanical actuation of another mechanical element.
The bimorph piezoelectric actuator is superior to a laminated piezoelectric actuator, in that it has a greater amount of displacement, lower power consumption, a faster response speed, and superior durability.
Meanwhile, the electromotive force (output power) developing in the bimorph piezoelectric actuator is small, and hence this bimorph piezoelectric actuator has hitherto been used for adjusting tracking of a VTR head, or the like.
In view of recent promotion of miniaturization, slimming-down, and weight reduction of electronic cameras such as video cameras, electronic still cameras, and the like, (including cameras incorporated into portable cellular phones and PDAs), the piezoelectric actuator has been used as a mechanical drive source of an imaging element.
For instance, a hand movement prevention mechanism for adjusting a focus by means of axially actuating an imaging element (a CCD or the like) by means of a piezoelectric actuator instead of actuation of a focus lens has been put forward (e.g., see Patent Documents 1 and 2). In Patent Document 2, a bimorph piezoelectric actuator is used as a mechanical drive source of the imaging element.
Patent Document 1 describes an embodiment where a piezoelectric actuator is connected directly to an imaging element and an embodiment where the displacement incited by the piezoelectric actuator is increased by means of a displacement-increasing mechanism using a leaf spring; and where an imaging element is actuated by means of restoration force of the leaf spring.
Patent Document 2 adopts a configuration where the displacement incited by the piezoelectric actuator is transmitted to an imaging element by way of an elastic flexible printed board; and where the displacement of the piezoelectric actuator is increased by means of restoration force of the flexible printed board.
Patent Document 1: JP-A-2000-307937
Patent Document 2: JP-A-2003-32537